Current clinical diagnostic methods for pneumonia typically take days or weeks and always require a sample from the patient, typically sputum. If sputum cannot be produced, it can sometimes be induced or lung lavage can be taken, both invasive techniques. Pneumonia is still one of the world's leading causes of death for children under the age of 5 according to the WHO and one of the top killers for adults in the USA, according to the CDC. Hence, there is a critical need for improved diagnostic tools to detect lung infections. Research groups at Dartmouth's Thayer School of engineering and the Vermont Lung Center have developed a technique allowing for rapid, non-invasive diagnosis of airway infections by analyzing infection-specific volatiles in the exhaled breath for singular infections, which can generate a diagnosis within minutes. The proposed work will complete the remaining experiments necessary before this technology is taken to a human population. The hypothesis is that that exhaled breath volatiles can be used to diagnose infections of the lung, and specifically, to distinguish between different pathogens, even during co-infection, for acute febrile illnesses. The hypothesis will be addressed in two specific aims: SA1: To determine whether breath volatile molecules can be used to distinguish between respiratory bacterial infections during clinical-relevant scenarios in a murine model. These experiments will demonstrate that a subset of breath molecules reflect infection etiology. The validity and specificity of the approach will be determined using confounding scenarios such as bacterial co-infection (in the lung and elsewhere) as well as during antibiotic treatment. This aim will also demonstrate determination of antibiotic susceptibility using breath for two organisms of high clinical interest (K. pneumoniae and S. aureus). SA2: To establish the utility of breath volatile molecules to distinguish between viral and bacterial infections. It will be determined how bacterial and viral co-infection affects the diagnostic precision of the exhaled breath analysis. Using influenza A virus, adenovirus and respiratory syncytial virus, it will be demonstrated that the immune system response to viral infection leads to the generation of molecules that can be detected in the breath and are diagnostic of infection etiology. All bacterial and viral experiment will use known human pathogens and will take place in well-developed animal models. The research in this proposal is innovative because it utilizes the best tools currently available to measure breath molecules in a systematic series of clinically-relevant experimental scenarios. The outcomes will represent a robust and substantial step towards a novel conceptual system for respiratory pathogen detection. The data from this study is expected to support forthcoming studies in humans and the development of an analytical device for use in the clinic. Ultimately, the technology shows promise for radically improved patient diagnosis, monitoring, and prognosis.